Method of forming laminate and method of manufacturing photovoltaic device

ABSTRACT

A method of forming a laminate and a method of manufacturing a photovoltaic device using the laminate are provided. The laminate forming method includes a first step of forming an intermediate layer on a base member, and a second step of forming a metal layer on the intermediate layer, the adhesion of the metal layer to the base member being lower than that of the intermediate layer, the reflectance of the metal layer being higher than that of the intermediate layer. The rate of formation of the metal layer is increased at an intermediate stage in the second step. The laminate thereby formed has improved characteristics and is capable of maintaining improved reflection characteristics and adhesion even under high-temperature and high-humidity conditions or during long-term use.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a laminate bylaminating an intermediate layer and a metal layer, a method of forminga laminate by laminating a metal layer and a metal oxide layer and amethod of manufacturing a photovoltaic device.

2. Related Background Art

As a photovoltaic device having an amorphous semiconductor layer formedof silicon, silicon-germanium or silicon carbide, or a semiconductorlayer containing crystal phases including those formed of a microcrystaland a polycrystal of such a material, a device having a reflecting layerformed on the back surface of the semiconductor layer to improve thecollection efficiency at long wavelengths has been used. It is desirablethat such a reflecting layer exhibit an effective reflectioncharacteristic closer to a band end of the semiconductor material, i.e.,in the range of 800 to 1200 nm. Examples of materials sufficientlysatisfying this condition are metals such as gold, silver, copper andaluminum, and alloys of these metals.

An arrangement using an optically transparent layer havingirregularities to achieve optical confinement has also been used. Ingeneral, attempts have been made to enable effective use of reflectedlight for improvement in short-circuit current density Jsc by forming alaminate in which a metal oxide layer having irregularities is providedbetween the reflecting layer and the semiconductor layer. Degradation incharacteristics due to a shunt path is prevented by providing such ametal oxide layer. Attempts have also been made to increase the opticalpath length for incident light in the semiconductor layer by providing ametal oxide layer having irregularities on the light incidence side of asemiconductor device for the purpose of enabling effective use ofreflected light for improvement in short-circuit current density Jsc.

For example, the achievement of an increase in short-circuit current byan optical confinement effect based on a combination of a reflectinglayer formed of silver atoms and having irregularities and a zinc oxidelayer is described in P-IA-15 a-SiC/a-Si/a-SiGe Multi-Bandgap StackedSolar Cells With Bandgap Profiling Sannomiya et al., Technical Digest ofthe International PVSEC-5, Kyoto, Japan, p387, 1990, and otherdocuments. Japanese Patent Application Laid-Open No. 8-217443 disclosesa method of uniformly forming a zinc oxide thin film having an improvedtransmittance by performing electrolysis in an aqueous solutioncontaining zinc ions and nitric acid ions.

In Japanese Patent Application Laid-Open No. 6-204515 is described theconstruction of stainless substrate/Ti/Ag/ZnO/Si and is disclosed use ofa Ti layer for improving the adhesion to the substrate.

Further improvements in the characteristics of the reflecting layer andthe metal oxide layer are being pursued to improve the characteristicsof photovoltaic devices. Also there is a problem that a photovoltaicdevice becomes deteriorated in photoelectric conversion characteristicsand durability, for example, due to a reduction in reflectance of ametal layer, a reduction in transmittance of a transparentelectroconductive layer or a reduction in adhesion between adjacentlayers in a case where the photovoltaic device is used underhigh-temperature and high-humidity conditions or used through a longperiod of time, in a case where a plurality of the photovoltaic devicesare used in a state of being connected in series, and where thephotovoltaic devices are maintained in a state of partially irradiatedwith light for a long time, or in a case where a voltage with a polarityopposite to that of the voltage generated by normal photoelectricconversion is applied to part of a plurality of photovoltaic devices notirradiated with light.

SUMMARY OF THE INVENTION

In view of the above-described problems, an object of the presentinvention is to provide a method of forming a laminate having improvedcharacteristics and capable of maintaining improved reflectioncharacteristics and adhesion even under high-temperature andhigh-humidity conditions or during long-term use, the laminate formed bythe method, and a photovoltaic device including the laminate.

The present invention provides a laminate forming method including afirst step of forming an intermediate layer on a base member, and asecond step of forming a metal layer on the intermediate layer, theadhesion of the metal layer to the base member being lower than that ofthe intermediate layer, the reflectance of the metal layer being higherthan that of the intermediate layer, wherein the rate of formation ofthe metal layer is increased at an intermediate stage in the secondstep.

The present invention provides a laminate forming method including afirst step of forming a metal layer on a base member to be processed,and a second step of forming a metal oxide layer on the metal layer,wherein the rate of formation of the metal layer is reduced at anintermediate stage in the first step, and the rate of formation of themetal oxide layer is increased at an intermediate stage in the secondstep.

The present invention also provides a method of manufacturing aphotovoltaic device, including a first step of forming an intermediatelayer on a base member, a second step of forming a metal layer on theintermediate layer, the adhesion of the metal layer to the base memberbeing lower than that of the intermediate layer, the reflectance of themetal layer being higher than that of the intermediate layer, and athird step of forming a semiconductor layer directly on the metal layeror with a metal oxide layer interposed between the semiconductor layerand the metal layer, wherein the rate of formation of the metal layer isincreased at an intermediate stage in the second step.

The present invention further provides a method of manufacturing aphotovoltaic device, including a first step of forming a metal layer ona base member to be processed, a second step of forming a metal oxidelayer on the metal layer, and a third step of forming a semiconductorlayer on the metal oxide layer, wherein the rate of formation of themetal layer is reduced at an intermediate stage in the first step, andthe rate of formation of the metal oxide layer is increased at anintermediate stage in the second step.

It is preferable to set the thickness of the intermediate layer withinthe range of 30 to 100 nm. It is preferable to set the rate of formationof the metal layer within the range of 0.5 to 4.0 nm/s before increasingthe rate of formation of the metal layer. It is preferable to increasethe rate of formation of the metal layer when the metal layer is formedon the intermediate layer to a thickness within the range of 1 nm to 100nm. It is preferable to set the rate of formation of the metal layerwithin the range of 0.5 to 4.0 nm/s by reducing the rate of formation ofthe metal layer. It is preferable to form the metal layer to a thicknesswithin the range of 1 to 100 nm and form the metal oxide layer on themetal layer after reducing the rate of formation of the metal layer. Itis preferable to set the rate of formation of the metal oxide layerwithin the range of 0.05 to 3.0 nm/s before increasing the rate offormation of the metal oxide layer. It is preferable to increase therate of formation of the metal oxide layer when the metal oxide layer isformed on the metal layer to a thickness within the range of 5 nm to 50nm. It is preferable to contain oxygen in the forming atmosphere atleast immediately before the completion of formation of the metal layerand immediately after the start of formation of the metal oxide layer.It is preferable to contain oxygen in the forming atmosphere afterreducing the rate of formation of the metal layer and before increasingthe rate of formation of the metal oxide layer.

A combination of the above-described laminate forming methods may beselected as desired to be used. Also, a combination of theabove-described photovoltaic device manufacturing methods may beselected as desired to be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example of a laminatemanufactured in accordance with the present invention;

FIG. 2 is a schematic cross-sectional view of an example of aphotovoltaic device manufactured in accordance with the presentinvention;

FIG. 3 is a schematic cross-sectional view of an example of a metallayer/metal oxide layer forming apparatus used in the present invention;

FIG. 4 is a schematic cross-sectional view of an example of asemiconductor layer forming apparatus used in the present invention;

FIG. 5 is a schematic cross-sectional view of another example of thephotovoltaic device manufactured in accordance with the presentinvention;

FIG. 6 is a schematic cross-sectional view of another example of thephotovoltaic device manufactured in accordance with the presentinvention; and

FIG. 7 is a schematic cross-sectional view of an example of a metaloxide layer forming apparatus used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors of the present invention eagerly made studies to solve theabove-described problems and found that a laminate formed by a laminateforming method including a first step of forming an intermediate layeron a base member, and a second step of forming a metal layer on theintermediate layer, the adhesion of the metal layer to the base memberbeing lower than that of the intermediate layer, the reflectance of themetal layer being higher than that of the intermediate layer, whereinthe rate of formation of the metal layer is increased at an intermediatestage in the second step, or by a laminate forming method including afirst step of forming a metal layer on a base member to be processed,and a second step of forming a metal oxide layer on the metal layer,wherein the rate of formation of the metal layer is reduced at anintermediate stage in the first step, and the rate of formation of themetal oxide layer is increased at an intermediate stage in the secondstep, and a photovoltaic device using the above-described laminate as asubstrate have improved characteristics and are capable of maintainingimproved reflection characteristics and adhesion even underhigh-temperature and high-humidity conditions or using long-term use.

The above-described constitution has effects described below.

The intermediate layer is formed to improve the adhesion between thelayers is improved in comparison with that in an arrangement in which ametal layer is formed directly on a base member, thereby ensuring thatdegradation in the functions of the laminate is limited even during usefor a long time or under high-temperature and high-humidity conditions.In a case where the above-described laminate is used as a substrate of aphotovoltaic device, a plurality of the photovoltaic devices may beconnected in series and used in a state of being partially irradiatedwith light for a long time. In such a case, a voltage with a polarityopposite to that of the voltage generated by normal photoelectricconversion is applied to part of the photovoltaic devices not irradiatedwith light. Even under such a condition, degradation in characteristicscan be limited.

Another effect of the provision of the intermediate layer is aninfluence on the surface configuration of the metal layer and the metaloxide layer. Details of the cause of this effect have not been madeclear. However, it is thought that the effect relates to changes in thefrequency of occurrence and the density of occurrence of growth nucleiin the metal layer and the rate of growth of the metal layer in anarbitrary direction from each nucleus due to wettability between thelayers and variation in interfacial free energy. In a case where thelaminate having the metal layer is used as a substrate of a photovoltaicdevice, the laminate has a role of a reflecting layer reflecting lightreaching the laminate to enable the light to be reused in thesemiconductor layer. Increasing the optical path length for reflectedlight in the semiconductor layer by having irregularities on the surfaceof the metal layer or the metal oxide layer so that the amount ofreusable light is increased is effective in optimizing theabove-described role of the laminate. If the thickness of theintermediate layer is insufficient, the effect obtained by insertion ofthe intermediate layer is not advantageously high. If the intermediatelayer is excessively thick, the uniformity of irregularities in thesurfaces of the metal layer and the metal oxide layer is reduced and itis difficult to grow optically effective irregularities. The cause ofthis phenomenon has not been made clear. This phenomenon is considereddue to occurrence of a nonuniform region such as a transition region inthe intermediate layer surface. It is thought that irregularityconfigurations in the surfaces of the metal layer and the metal oxidelayer can be made uniform and in a desirable condition by selecting thethickness of the intermediate layer while considering theabove-described points, and that it is important to maintain thetemperature of the formation surface above a certain point at the timeof formation of the intermediate layer and to thereby promote thesurface reaction in providing a basis for improving the adhesion andgrowing irregularities in the surfaces of the metal layer and the metaloxide layer.

The inventors of the present invention eagerly studied by consideringthe above-described points and found that it is preferable to set thethickness of the intermediate layer within the range of 30 nm to 100 nm,and it is also preferable to set the temperature of the formationsurface of the intermediate layer to 300° C. or higher.

The adhesion between the metal layer and the intermediate layer can beimproved by increasing the rate of formation of the metal layer in anintermediate stage of formation of the metal layer on the intermediatelayer. Further, the conditions of the surfaces of the metal layer andthe metal, oxide layer can be improved thereby. Preferably, the rate offormation of the metal layer is increased when the metal layer is formedto a thickness within the range of 1 to 100 nm on the intermediatelayer.

To achieve the effect of improving the adhesion between the metal layerand the intermediate layer, it is preferable to increase the formationrate when the metal layer is formed to a thickness of 1 nm or more onthe intermediate layer. From the viewpoint of achieving the effect ofgrowing an irregularity configuration in the metal layer surface andfrom the viewpoint of productivity, it is preferable to limit the rangeof the thickness of the metal layer formed before increasing theformation rate to 100 nm or less.

It is preferable to form the metal layer at a rate of 4.0 nm/s or lowerbefore the formation rate is increased. If importance is attached to theproductivity, it is preferable to form the metal layer at a rate of 0.5nm/s or higher before the formation rate is increased, and thetemperature of the formation surface of the metal layer is preferably300° C. or higher.

The method of reducing the formation rate at an intermediate stage inthe step of forming the metal layer on the intermediate layer andforming the metal oxide layer on the metal layer is preferable becausethe adhesion between the metal layer and the metal oxide layer isimproved. It is thought that in a case where oxygen is contained in theatmosphere for forming the metal layer after the formation rate has beenreduced, in particular, at least part of the metal layer is oxidized andstabilization of the interfacial structure and, hence, an improvement inadhesion at the interface can be achieved by the effect of thisoxidation and the effect of prevention of diffusion of metal atomsthrough the metal oxide layer. More preferably, the metal layer isformed to a thickness within the range of 1 to 100 nm after reducing therate of formation of the metal layer, and the metal oxide layer is thenformed on the metal layer. To achieve the above-described improvementeffect, it is preferable to set the rate of formation of the metal layerto 4.0 nm/s or lower after reducing the formation rate. From theviewpoint of productivity, setting the formation rate to 0.5 nm/s orhigher is preferred and setting the temperature of the formation surfaceof the metal layer 300° C. or higher is also preferred.

To achieve the effect of improving the adhesion between the metal layerand the metal oxide layer, it is preferable to set the thickness of themetal layer formed after reducing the formation rate to 1 nm or larger.From the viewpoint of achieving the effect of growing an irregularityconfiguration in the metal layer surface and from the viewpoint ofproductivity, it is preferable to limit the range of the thickness ofthe metal layer after reducing the formation rate to 100 nm.

Increasing the rate of formation of the metal oxide layer at anintermediate stage in the step of forming the metal oxide layer on themetal layer is preferable because the adhesion between the metal layerand the metal oxide layer is improved. Containing oxygen in theatmosphere for forming the metal oxide layer before increasing theformation rate is particularly preferable. If the material of the metaloxide layer is, for example, zinc oxide, the zinc oxide layer istransparent in the visible region since its band gap is about 3.3 eV. Ifthe zinc oxide layer is formed so as to have a zinc-excessive-typecomposition due to intrusion of zinc atoms into the lattice, oxygen atomvacancies in the lattice, etc., an excess amount of zinc forms a donorlevel such that the zinc oxide layer functions as a transparentelectroconductive layer having suitable electrical conductivity. It isthought that an increase in the rate of formation of the metal oxidelayer at an intermediate stage of formation of the metal oxide layer onthe metal surface contributes to an improvement in adhesion between themetal layer and the metal oxide layer in comparison with a case in whichthe metal oxide layer is formed at a constant rate on the metal layer.This thought to be because the formation of an inconsistency region inthe interface due to the difference between the metal layer having aclose-packed structure or a like structure and the metal oxide layer nothaving a close-packed structure is limited. In particular, this isthought to be because if oxygen is contained in the atmosphere forforming the metal oxide layer before increasing the formation rate, theratio of the amount of oxygen and the amount of zinc in zinc oxidebecomes closer to the stoichiometric ratio and the excess amount of zincin zinc oxide, particularly the amount of zinc ions existing in thelattice is reduced to reduce lattice stress in zinc oxide in thejunction region between the metal layer and the metal oxide layer. Fromthe viewpoint of achieving the above-described effect and avoidingdegradation in the functions of the transparent electroconductive layer,it is preferable to set within the range of 5 to 50 nm the thickness ofthe metal oxide layer formed before increasing the formation rate.

To achieve the effect of limiting the formation of the inconsistencyregion between the metal layer and the metal oxide layer, it ispreferable to set to 5 nm or larger the thickness of the metal oxidelayer formed before increasing the formation rate. From the viewpoint ofproductivity, limiting the thickness of the metal oxide layer formedbefore increasing the formation rate is preferred. If the metal oxidelayer is formed under an oxygen containing condition before theformation rate is increased, and if the thickness of the metal oxidelayer formed before increasing the formation rate is excessively large,the resistivity of the metal oxide layer is considerably high since theoxygen content is increased to increase the resistivity of the metaloxide layer. From consideration of the above, it is preferable to setthe thickness of the metal oxide layer formed before increasing theformation rate within the range not exceeding 50 nm.

To achieve the above-described improvement effect, it is preferable toset rate of formation of the metal oxide layer before increasing theformation rate to 3.0 nm/s or lower. From consideration of productivity,setting the formation rate to 0.05 nm/s or higher is preferred andsetting the temperature of the formation surface of the metal oxidelayer to 200° C. or higher is also preferred. In particular, if themetal oxide layer is formed by setting the temperature of its formationsurface below the temperature of the formation surface of the metallayer, internal stress after the formation of the laminate is reduced.Therefore this setting is preferable.

Components of a photovoltaic device using the laminate of the presentinvention as a substrate will be described below.

FIGS. 1 and 2 are schematic cross-sectional views of a substrate and anexample of a photovoltaic device in accordance with the presentinvention. In FIGS. 1 and 2, a substrate is indicated by 101, asemiconductor layer by 102, a transparent electroconductive layer by103, and a current collecting electrode by 104. The substrate 101 isconstituted by a base member 101-1, an intermediate layer 101-2, a metallayer 101-3 and a metal oxide layer 101-4.

(Base Member)

As the base member 101-1, a plate or a sheet made of a metal, a resin, aglass, a ceramic or a semiconductor is favorably used. The base member101-1 may have fine irregularities in its surface. If the base member101-1 may be formed from a member of an elongated shape which can beformed by continuous film forming using a roll-to-roll method. Amaterial having flexibility, e.g., stainless steel or a polyimide isparticularly preferred as a material for the base member 101-1.

(Intermediate Layer)

As a material for the intermediate layer 101-2 which is a constituent ofthe present invention, a material is selected which has a degree ofadhesion to the base member higher than the degree of adhesion betweenthe base member and the metal layer, and also has suitable adhesion tothe metal layer. The intermediate layer is capable of influencing thesurface configuration of the metal layer formed on the intermediatelayer. The material and thickness of the intermediate layer are selectedso as to satisfy the above-described conditions, thereby enablingsuitable irregularities to be uniformly formed in the surfaces of themetal layer and the metal oxide layer while maintaining the desiredreflectivity. The material of the intermediate layer is selected fromtransition metals or oxides of metals satisfying the above-describedconditions. Nickel, chromium, titanium, ZnO, SnO₂, In₂O₃, ITO(In₂O₃+SnO₂) or the like is favorably used as a material for theintermediate layer. Evaporation, sputtering or electrodeposition isfavorably used as a method of forming the intermediate layer. Inexamples of the present invention described below, a base member havingsuch an intermediate layer corresponds to the base member to beprocessed. However, the base member to be processed is not limited tothis.

(Metal Layer)

The metal layer 101-3 has a role of an electrode and a role of areflecting layer for reflecting light not absorbed by the semiconductorlayer 102 to enable reuse of this light in the semiconductor layer 102.As a material for the metal layer 101-3, Al, Cu, Ag, Au, CuMg, AlSi orthe like is favorably used. Evaporation, sputtering or electrodepositionis favorably used as a method of forming the metal layer 101-3.Preferably, the metal layer 101-3 has irregularities in its surface. Theoptical path length for reflected light in the semiconductor layer 102is thereby increased to increase short-circuit current. In forming themetal layer, it is preferable to use a method of reducing the rate offormation of the metal layer in a region where the metal layer contactsthe intermediate layer and/or in a region where the metal layer contactsthe metal oxide layer. Also, it is preferable to contain oxygen in aforming atmosphere for forming in the region where the metal layercontact the metal oxide layer.

(Metal Oxide Layer)

The metal oxide layer 101-4 has a role of increasing diffused reflectionof incident light and reflected light to increase the optical pathlength in the semiconductor layer 102. The metal oxide layer 101-4 alsohas a role of preventing shunt in the photovoltaic device caused bydiffusion or migration of elements in the intermediate layer 101-2 andthe metal layer 101-3 into the semiconductor layer 102. Further, themetal oxide layer 101-4 has a suitable resistance to have a role ofpreventing short-circuit due to a defect such as pin holes in thesemiconductor layer. Preferably, the metal oxide layer 101-4 hasirregularities in its surface, as does the metal layer 101-3.Preferably, the metal oxide layer 101-4 is a layer of anelectroconductive oxide such as ZnO or ITO, and is formed byevaporation, sputtering, CVD, electrodeposition or the like. Some ofthese forming methods may be used in combination if necessary. Amaterial for changing the electric conductivity may be added to theabove-described electroconductive oxide. In forming the metal oxidelayer, it is preferable to use a method of reducing the rate offormation of the metal oxide layer in a region where the metal oxidelayer contacts the metal layer. Also, it is preferable to contain oxygenin a forming atmosphere for forming in the region where the metal oxidelayer contacts the metal layer.

The formation of each of the metal layer and the metal oxide layer bysputtering is largely influenced by the kind of forming method, the kindand flow rate of a gas, the internal pressure, the applied electricpower, the forming rate, the temperature of the formation surface, etc.In the case of forming zinc oxide film by DC magnetron sputtering usinga zinc oxide target, kinds of gas used are, for example, some of Ar, Ne,Kr, Xe, Hg, and O₂, and it is desirable that the flow rate, whichdepends on the size of the apparatus and the exhaust rate, be 1 to 100cm³/min (normal) if the capacity of the film forming space is 20 liters.It is also desirable that the internal pressure at the time of filmforming be 10 mPa to 10 Pa.

Preferably, as a condition under which the metal oxide layer formed ofzinc oxide is formed by electrodeposition, an aqueous solutioncontaining nitric acid ions and zinc ions is used in acorrosion-resistant container. It is desirable that the concentration ofnitric acid ions and zinc ions be within the range of 0.001 to 1.0mol/l. It is more desirable that the concentration be within the rangeof 0.01 to 0.5 mol/l. It is further desirable that the concentration bewithin the range of 0.1 to 0.25 mol/l. Sources for supplying nitric acidions and zinc ions are not limited to particular kinds. Zinc nitrate maybe used as a source for supplying both these kinds of ions, and amixture of a water-soluble nitrate such as ammonium nitrate, which is anitric acid ion supply source, and a zinc salt such as zinc sulfate,which is a zinc ion supply source, may be used. Further, it ispreferable to add a carbohydrate to an aqueous solution of each of thesesupply source materials for the purpose of limiting abnormal growth andimproving adhesion. Any carbohydrate may be added for this purpose.However, a monosaccharide such as glucose (grape sugar) or fructose(fruit sugar), a disaccharide such as maltose (malt sugar) or saccharose(cane sugar), a polysaccharide such as dextrin or starch, or a mixtureof some of these materials may be used. It is desirable that the amountof carbohydrate in the aqueous solution, which depends on the kind ofcarbohydrate, be within the range of 0.001 to 300 g/l. It is moredesirable that the amount of carbohydrate be within the range of 0.005to 100 g/l. It is further desirable that the amount of carbohydrate bewithin the range of 0.01 to 60 g/l. Preferably, in the case of forming alayer of zinc oxide as the metal oxide layer by electrodeposition, thebase member on which the metal oxide layer is formed is used as acathode in the aqueous water solution, while zinc, platinum, carbon orthe like is used as an anode. Preferably, the density of current flowingthrough the load resistor is 10 mA/dm² to 10 A/dm².

(Substrate)

The substrate 101 is formed by laminating the intermediate layer 101-2,the metal layer 101-3 and the metal oxide layer 101-4 on the base member101-1 as desired by the above-described methods. An insulating layer maybe formed on the substrate 101 for the purpose of facilitatingintegration of the device.

(Semiconductor Layer)

As a main material of the silicon semiconductor and the semiconductorlayer 102 of the present invention, Si in an amorphous phase or acrystalline phase or a mixture of Si in an amorphous phase and Si in acrystalline phase is used. An alloy of Si and C or Ge may be used inplace of Si. The semiconductor layer 102 also contains hydrogen and/orhalogen atoms. Preferably, the content of these elements is 0.1 to 40atomic percent. The semiconductor layer 102 may further contain oxygenand nitrogen. To form the semiconductor layer as a p-type semiconductorlayer, a group III element is contained. To form the semiconductor layeras an n-type semiconductor layer, a group V element is contained. Eachof the p-type and n-type semiconductor layers has, as its electriccharacteristics, activation energy of preferably 0.2 eV or less, mostpreferably 0.1 eV or less, and a resistivity of preferably 100 Ωcm orless, most preferably 1 Ωcm or less. It is preferred that in the case ofa stack cell (a photovoltaic device having a plurality of pin junctions)the i-type semiconductor layer in a pin junction closer to the lightincidence side have a wider bandgap, and the bandgap be reduced at aremoter pin junction. It is also preferred that in each i layer thebandgap minimum value exist on the p layer side of a center in the filmthickness direction. A crystalline semiconductor lower in absorption oflight or a semiconductor of a wider bandgap is suitable for a dopedlayer (p-type layer or n-type layer) on the light incidence side. Forexample, a stack cell formed by stacking two groups of layers formingpin junctions has, as a combination of i-type silicon semiconductorlayers, (an amorphous semiconductor layer and a semiconductor layercontaining a crystalline phase) or (a semiconductor layer containing acrystalline phase and a semiconductor layer containing a crystallinephase) in the order from the light incidence side. A stack cell formedby stacking three groups of layers forming pin junctions has, as acombination of i-type silicon semiconductor layers, (an amorphoussemiconductor layer, an amorphous semiconductor layer and asemiconductor layer containing a crystalline phase), (an amorphoussemiconductor layer, a semiconductor layer containing a crystallinephase and a semiconductor layer containing a crystalline phase), or (asemiconductor layer containing a crystalline phase, a semiconductorlayer containing a crystalline phase and a semiconductor layercontaining a crystalline phase) in the order from the light incidenceside. Preferably, the i-type semiconductor layer has an absorptioncoefficient (α) of 5000 cm⁻¹ or greater with respect to light (630 nm),an optical conductivity (σp) of 10×10⁻⁵ S/cm or higher under irradiationwith pseudo-solar light by a solar simulator (AM 1.5, 100 mW/cm²), adark conductivity (σd) of 10×10⁻⁶ S/cm or lower, and Urbach energy of 55meV or lower according to a constant photocurrent method (CPM). As thei-type semiconductor layer, one slightly exhibiting the behavior of thep type or n type can be used.

Further description will be made of the semiconductor layer 102 which isa constituent of the present invention. FIG. 5 is a schematiccross-sectional view of a semiconductor layer 102 having one group oflayers forming a pin junction. This semiconductor layer is an example ofthe semiconductor layer in accordance with the present invention. Alayer indicated by 102-1 in FIG. 5 is an amorphous n-type semiconductorlayer. An i-type semiconductor layer 102-2 and a p-type semiconductorlayer 102-3 containing a crystalline phase are further laminated.Preferably, in semiconductor layers having a plurality of pin junctions,at least one of the groups of layers having pin junctions has theabove-described construction.

(Method of Forming Semiconductor Layer)

A radiofrequency plasma CVD method is method is suitable for forming thesilicon semiconductor of the present invention and the above-describedsemiconductor layer 102. An example of a suitable process for formingthe semiconductor layer 102 by a radiofrequency plasma CVD method willbe described.

-   (1) The interior of a forming chamber (vacuum chamber) which can be    maintained in a depressurized state is depressurized to a    predetermined pressure.-   (2) A raw-material gas and a material gas such as a diluent gas are    introduced into the forming chamber, and the pressure in the forming    chamber is set to a predetermined pressure by evacuating the forming    chamber with a vacuum pump.-   (3) The substrate 101 is set to a predetermined temperature by using    a heater.-   (4) A radiofrequency wave oscillated by a radiofrequency power    source is introduced into the forming chamber. As a method of    introducing the radiofrequency wave into the forming chamber, a    method of guiding the radiofrequency wave through a waveguide and    introducing the radiofrequency wave into the forming chamber through    a window made of a dielectric such as an alumina ceramic, or a    method of guiding the radiofrequency wave through a coaxial cable    and introducing the radiofrequency wave into the forming chamber by    using a metal electrode may be used.-   (5) The raw-material gas is decomposed by generating a plasma in the    forming chamber to form a semiconductor layer on substrate 101    placed in the forming chamber. This process is repeated a certain    number of times to form semiconductor layer 102.

The following are examples of suitable conditions for forming thesilicon semiconductor of the present invention and the above-describedsemiconductor layer 102 are as described below. The temperature of theformation surface in the forming chamber is 100 to 450° C., the pressureis 50 mPa to 1500 Pa, and the radiofrequency power is 0.001 to 1W/cm³.

An example of a raw-material material gas suitable for forming thesilicon semiconductor of the present invention and the above-describedsemiconductor layer 102 is a gasifiable compound such as SiH₄, Si₂H₆ orSiF₄ containing silicon atoms. In the case of forming an alloysemiconductor, it is desirable to add to a row-material gas a gasifiablecompound such as GeH₄ or CH₄ containing Ge or C. It is desirable thatthe raw-material gas be diluted with a diluent gas when introduced intothe forming chamber. The diluent gas is, for example, H₂ or He. Further,a gasifiable compound containing nitrogen or oxide for example may beadded as a raw-material gas or a diluent gas. B₂H₆, BF₃ or the like maybe used as a dopant gas for forming a p-type semiconductor layer. Also,PH₃, PF₃ or the like may be used as a dopant gas for forming an n-typesemiconductor layer. In the case of forming a thin film in a crystallinephase or a layer such as an SiC layer lower in absorption of or having awider bandgap, it is preferable to increase the proportion of thediluent gas relative to that of the raw-material gas and to introduce aradiofrequency wave at a comparatively high power.

(Transparent Electroconductive Layer)

The transparent electroconductive layer 103 is an electrode on the lightincidence side and can also have a role of antireflection film if itsthickness is set to a suitable value. It is necessary for thetransparent electroconductive layer 103 to have a high transmittance inthe absorbable wavelength region of the semiconductor layer 102 and tohave a low resistivity. The transmittance at 550 nm is preferably 80% orhigher, more preferably 85% or higher. As a material for the transparentelectroconductive layer 103, ITO, ZnO, In₂O₃ or the like is favorablyused. As a method for forming the transparent electroconductive layer103, evaporation, CVD, spraying, spin-on, immersion or the like isfavorably used. A material for changing the conductivity may be added toeach of the above-described materials.

(Current Collecting Electrode)

The current collecting electrode 104 is provided on the transparentelectrode 103 to improved the current collection efficiency. As a methodof forming the current collecting electrode 104, a method of forming ametal in an electrode pattern by sputtering using a mask, a method ofprinting an electroconductive conductive paste or a soldering paste or amethod of fixing a metal wire by an electroconductive paste is favorablyused.

A protective layer may be formed on two surfaces of the photovoltaicdevice if necessary. A reinforcing member such as a steel plate may alsobe provided, for example, on the back surface (opposite from the lightincidence side) of the photovoltaic device.

EXAMPLES

Solar cells will be described as examples of the photovoltaic device ofthe present invention. However, the present invention is not limited bythe examples described below.

Example 1

A band-like base member 304 made of stainless steel (SUS430BA) (40 cmwide, 200 m long and 0.125 mm thick) was sufficiently degreased andcleansed. Thereafter, a substrate formed of an intermediate layer 101-2,a metal layer (A) 101-3A, a metal layer (B) 101-3B, a metal layer (C)101-3C, a metal oxide layer (A) 101-4A and a metal oxide layer (B)101-4B was formed by using a metal layer/metal oxide layer formingapparatus 301 shown in FIG. 3.

FIG. 3 is a schematic cross-sectional view of an example of the metallayer/metal oxide layer forming apparatus 301 for manufacturing thesubstrate of the photovoltaic device of the present invention. The metallayer/metal oxide layer forming apparatus 301 shown in FIG. 3 isconstructed by connecting a substrate feed-out container 302, anintermediate layer forming vacuum container 311, a metal layer (A)forming vacuum container 312, a metal layer (B) forming vacuum container313, a metal layer (C) forming vacuum container 314, a metal oxide layer(A) forming vacuum container 315, a metal oxide layer (B) forming vacuumcontainer 316 and a substrate take-up container 303 through gas gates.In this semiconductor layer forming apparatus 301, the band-like basemember 304 is set so as to extend through each forming vacuum container.The band-like base member 304 is unwound from a bobbin placed in thesubstrate feed-out container 302 and is wound around another bobbin inthe substrate take-up container 303.

Targets are provided as cathodes 341 to 346 in the forming vacuumcontainers. Sputtering from the targets can be performed by using DCpower supplies 351 to 356 to form intermediate layer 101-2, metal layer(A) 101-3A, metal layer (B) 101-3B, metal layer (C) 101-3C, metal oxidelayer (A) 101-4A and metal oxide layer (B) 101-4B on the base member.Gas introducing pipes 331 to 336 for introducing sputtering gases arerespectively connected to the forming vacuum containers.

While the metal layer/metal oxide layer forming apparatus 301 shown inFIG. 3 has six forming vacuum containers, it is not necessary to performfilm forming in all the forming vacuum containers in the examplesdescribed below and it is possible to select execution/non-execution offorming in each forming vacuum container according to the layerconstruction of the substrate to be manufactured. In each formingcontainer, a film forming region adjusting plate (not shown) foradjusting the area of contact between the base member 304 and thedischarge space is provided. It is possible to adjust the thickness ofthe semiconductor layer formed in each forming container by adjustingthe film forming region adjusting plate.

The base member 304 was placed in the metal layer/metal oxide layerforming apparatus 301 and each forming container was evacuated until thepressure therein became equal to 1.0 mPa or lower.

Thereafter, sputtering gases were supplied through the gas introducingpipes 331 to 336 while the evacuation system was being operated.Simultaneously, Ar gas was supplied as a gate gas at 50 cm³/min (normal)to each gas gate through a gate gas supply pipe (not shown). In thissate, the pressure in each forming vacuum container was adjusted to apredetermined pressure by adjusting the evacuation ability of theevacuation system. Forming conditions were as shown in Table 1.

When the pressure in each forming vacuum container was stabilized, themovement of the base member 304 in the direction from the substratefeed-out container 302 toward the substrate take-up container 303 wasstarted. While the base member 304 was being moved, an infrared lampheater in each forming vacuum container was energized to adjust thetemperature of the formation surface of the base member 304 to the valueshown in Table 1. A titanium target having a purity of 99.99 wt % wasused as cathode electrode 341. A silver target having a purity of 99.99wt % was used as each of cathode electrodes 342 to 344. A zinc oxidetarget having a purity of 99.99 wt % was used as each of cathodeelectrodes 345 and 346. Sputtering power shown in Table 1 was applied toeach cathode electrode. Intermediate layer 101-2 formed of titanium (50nm thick, at a forming rate of 1.5 nm/s), metal layer (A) 101-3A formedof silver (50 nm thick, at a forming rate of 1.5 nm/s), metal layer (B)101-3B formed of silver (750 nm thick, at a forming rate of 8.0 nm/s),metal layer (C) 101-3C formed of silver (50 nm thick, at a forming rateof 1.5 nm/s), metal oxide layer (A) 101-4A formed of zinc oxide (10 nmthick, at a forming rate of 1.0 nm/s) and metal oxide layer (B) 101-4Bformed of zinc oxide (2000 nm thick, at a forming rate of 10.0 nm/s)were formed, thus forming the band-like substrate (Example 1-1).

Next, the pin-type photovoltaic device shown in FIG. 5 was formed by aprocess described below, using a semiconductor layer forming apparatus201 shown in FIG. 4. FIG. 5 is a schematic cross-sectional view of anexample of a photovoltaic device having the silicon semiconductor of thepresent invention. In FIG. 5, the same components as those shown in FIG.1 are indicated by the same reference characters. Description for thesame components will not be repeated. The semiconductor layer of thisphotovoltaic device is formed of an amorphous n-type semiconductor layer102-1, an i-type semiconductor layer 102-2 containing a crystallinephase, and a p-type semiconductor layer 102-3 containing a crystallinephase. That is, this photovoltaic device is a pin-type single-cellphotovoltaic device.

FIG. 4 is a schematic cross-sectional view of an example of asemiconductor layer forming apparatus 201 for manufacturing the siliconsemiconductor and the photovoltaic device of the present invention. Thesemiconductor layer forming apparatus 201 shown in FIG. 4 is constructedby connecting a substrate feed-out container 202, semiconductor formingvacuum containers 211 to 218 and a substrate take-up container 203through gas gates. In this semiconductor layer forming apparatus 201, aband-like substrate 204 is set so as to extend through each containerand each gas gate. The band-like substrate 204 is unwound from a bobbinplaced in the substrate feed-out container 202 and is wound aroundanother bobbin in the substrate take-up container 203.

The semiconductor forming vacuum containers 211 to 218 respectively haveforming chambers in which glow discharge is caused by application ofradiofrequency power from radiofrequency power supplies 251 to 258 todischarging electrodes 241 to 248. Raw-material gases are therebydecomposed to form semiconductor layers on the substrate 204. Gasintroducing pipes 231 to 238 for introducing raw-material gases anddiluent gases are respectively connected to the semiconductor formingvacuum containers 211 to 218.

While the semiconductor layer forming apparatus 201 shown in FIG. 4 haseight semiconductor forming vacuum devices, it is not necessary to causeglow discharge in all the semiconductor forming vacuum containers in theexamples described below and it is possible to selectexecution/non-execution of glow discharge in each container according tothe layer construction of the photovoltaic device to be manufactured. Ineach semiconductor forming device, a film forming region adjusting plate(not shown) for adjusting the area of contact between the substrate 204and the discharge space in each forming chamber is provided. It ispossible to adjust the thickness of the semiconductor layer formed ineach container by adjusting the film forming region adjusting plate.

The bobbin around which the substrate 204 was wound was set in thesubstrate feed-out container 202 and was led to the substrate take-upcontainer 203 via the entrance-side gas gate, the substrate layerforming vacuum containers 211 to 218 and the exit-side gas gate, andtension adjustment was performed so that the band-like substrate 204 didnot sag. The substrate feed-out container 202, the semiconductor layerforming vacuum containers 211 to 218 and the substrate take-upcontainers 203 were evacuated to 1.0 mPa or lower by an evacuationsystem formed by a vacuum pump (not shown).

Subsequently, raw-material gases and diluent gases were supplied to thesemiconductor layer forming vacuum containers 211 to 215 through the gasintroducing pipes 231 to 235 while the evacuation system was beingoperated.

Also, H₂ gas was supplied at 200 cm³/min (normal) to the semiconductorlayer forming vacuum containers other than the semiconductor layerforming vacuum containers 211 to 215 through the gas introducing pipes.Simultaneously, H₂ gas was supplied as a gate gas at 500 cm³/min(normal) to each gas gate through a gate gas supply pipe (not shown). Inthis state, the pressure in each of the semiconductor layer formingvacuum containers 211 to 215 was adjusted to a desired pressure byadjusting the evacuation ability of the evacuation system. Formingconditions were as shown in Table 2.

When the pressure in each of the semiconductor layer forming vacuumcontainers 211 to 215 was stabilized, the movement of the substrate 204in the direction from the substrate feed-out container 202 toward thesubstrate take-up container 203 was started.

Next, radiofrequency waves were introduced from the radiofrequency powersupplies 251 to 255 to the discharging electrodes 241 to 245 in thesemiconductor layer forming vacuum containers 211 to 215 to cause glowdischarge in the forming chambers in the semiconductor layer formingvacuum containers 211 to 215, thereby forming an amorphous n-typesemiconductor layer (50 nm thick), an i-type semiconductor layer (1.5 μmthick) containing a crystalline phase and a p-type semiconductor layer(10 nm thick) containing a crystalline phase on the substrate 204. Thephotovoltaic device was thus formed (Example 1-2).

In this process, radiofrequency power at a frequency of 13.56 MHz and apower density of 5 mW/cm³ was introduced into the semiconductor formingvacuum container 211, radiofrequency power at a frequency of 60 MHz anda power density of 300 mW/cm³ into the semiconductor forming vacuumcontainers 212 to 214, and radiofrequency power at a frequency of 13.56MHz and a power density of 30 mW/cm³ into the semiconductor formingvacuum container 215. The band-like photovoltaic device thus formed wasworked into 36×22 cm solar cell modules (Example 1-3) by continuousmodulation apparatus (not shown).

Example 2

Substrates, photovoltaic devices and solar cell modules (Example 2-1,Example 2-2, Example 2-3) were made by the same process as that inExample 1 except that oxygen was not introduced at the time of formingof metal layer (C) 101-3C and metal oxide layer (A) 101-4A.

Example 3

Substrates, photovoltaic devices and solar cell modules (Example 3-1,Example 3-2, Example 3-3) were made by the same process as that inExample 1 except that metal layer (A) 101-3A was not formed.

Example 4

Substrates, photovoltaic devices and solar cell modules (Example 4-1,Example 4-2, Example 4-3) were made by the same process as that inExample 1 except that metal layer (C) 101-3C was not formed.

Example 5

Substrates, photovoltaic devices and solar cell modules (Example 5-1,Example 5-2, Example 5-3) were made by the same process as that inExample 1 except that metal oxide layer (A) 101-4A was not formed.

Comparative Example 1

Substrates, photovoltaic devices and solar cell modules (ComparativeExample 1-1, Comparative Example 1-2, Comparative Example 1-3) were madeby the same process as that in Example 1 except that intermediate layer101-2 was not formed.

Comparative Example 2

Substrates, photovoltaic devices and solar cell modules (ComparativeExample 2-1, Comparative Example 2-2, Comparative Example 2-3) were madeby the same process as that in Example 1 except that the rate offormation of metal layer (A) 101-3A and metal layer (C) 101-3C was thesame as the rate of formation of metal layer (B) 101-3B, and that therate of formation of metal oxide layer (A) 101-4A was the same as therate of formation of metal oxide layer (B) 101-4B.

The reflectances of the substrates made in the examples of the presentinvention and the comparative examples were measured with respect tolight of 800 nm, and the adhesion between the base member, the metallayer and the metal oxide layer was examined by using a grid tape method(the intervals between cuts: 1 mm; the number of squares: 100). Further,sub-cells were formed by making 100 transparent electrodes having a sizeof 1 cm² and current collectors on the photovoltaic devices in theexamples of the present invention and the comparative examples, and thephotoelectric conversion efficiency of each sub-cell was measured byusing the solar simulator (AM 1.5, 100 mW/cm²), thereby examining theaverage and uniformity of the photoelectric conversion efficiency.Further, the photoelectric conversion efficiency of each of the solarcell modules made in the examples of the present invention and thecomparative examples was measured, the solar cell module was thereafterplaced in a dark place at a temperature of 85° C. and a humidity of 85%and maintained for 500 hours while a reverse bias of 10V was beingapplied. Thereafter, the photoelectric conversion efficiency was againmeasured to examine a change in photoelectric conversion efficiency dueto application of the reverse bias under high-temperature andhigh-humidity conditions. Table 3 shows the results of theseexaminations.

It can be understood that the substrates, the photovoltaic devices andthe solar cell modules in Examples 1 to 5 of the present invention weresuperior to those in the comparative examples, as shown in Table 3. SEMobservation of the states of portions peeled by the grid tape method inComparative Example 1 was also performed, thereby confirming thatseparation was caused between the stainless base member and the silvermetal layer. From the above, it can be understood that the substratesand the photovoltaic devices using the laminates in accordance with thepresent invention and the solar cell modules including the substratesand the photovoltaic devices have improved qualities. In particular, thesubstrate, the photovoltaic device and the solar cell module in Example1 are excellent in each evaluation item.

Example 6

Substrates and solar cell modules (Examples 6-1 to 6-5) were made in thesame manner as in Example 1 except that the thickness of intermediatelayer 101-2 was changed to 10 nm, 30 nm, 80 nm, 100 nm, and 150 nm. Thereflectance of the substrates thereby made was measured with respect tolight of 800 nm, the adhesion in the substrates was examined by the gridtape method, and the photoelectric conversion efficiency of the solarcell modules was measured by using the solar simulator (AM 1.5, 100mW/cm²). The results of the measurement and examination in Example 6were shown in Table 4 together with the results with respect toComparative Example 1 made without the intermediate layer.

It can be understood that the substrates and the photovoltaic devicesusing the laminates in accordance with the present invention and thesolar cell modules including the substrates and the photovoltaic deviceshave improved qualities, as shown in Table 4. In particular, thesubstrates, the photovoltaic devices and the solar cell modules havingthe thickness of the intermediate layer within the range of 30 nm to 100nm are excellent in reflectance, adhesion and photoelectric conversionefficiency.

Example 7

Substrates and solar cell modules (Examples 7-1 to 7-6) were made in thesame manner as in Example 1 except that the rate of formation of metallayer (A) 101-3A was changed to 0.3 nm/s, 0.5 nm/s, 1.0 nm/s, 2.0 nm/s,4.0 nm/s, and 5.0 nm/s. The reflectance of the substrates thereby madewas measured with respect to light of 800 nm, and the photoelectricconversion efficiency of the solar cell modules was measured by usingthe solar simulator (AM 1.5, 100 mW/cm²). Further, each solar cellmodule was placed in a dark place at a temperature of 85° C. and ahumidity of 85% and maintained for 500 hours while a reverse bias of 10Vwas being applied. Thereafter, the photoelectric conversion efficiencywas again measured to examine a change in photoelectric conversionefficiency due to application of the reverse bias under high-temperatureand high-humidity conditions. Table 5 shows the results of thesemeasurements.

It can be understood that the substrates and the photovoltaic devicesusing the laminates in accordance with the present invention and thesolar cell modules including the substrates and the photovoltaic deviceshave improved qualities, as shown in Table 5. It can also be understoodthat the substrates, the photovoltaic devices and the solar cell modulesformed by setting the rate of formation of metal layer (A) to a valuenot higher than 4.0 nm/s have particularly improved qualities in termsof reflectance, photoelectric conversion efficiency and the results ofthe high-temperature and high-humidity reverse bias application test.Also, those formed by setting the rate of formation of metal layer (A)to 0.5 nm/s or higher are particularly advantageous in terms ofproductivity since metal layer (A) can be formed in a shorter time incomparison with metal layer (B).

Example 8

Substrates and solar cell modules (Examples 8-1 to 8-6) were made in thesame manner as in Example 1 except that the rate of formation of metallayer (C) 101-3C was changed to 0.3 nm/s, 0.5 nm/s, 1.0 nm/s, 2.0 nm/s,4.0 nm/s, and 5.0 nm/s. The reflectance of the substrates thereby madewas measured with respect to light of 800 nm, and the photoelectricconversion efficiency of the solar cell modules was measured by usingthe solar simulator (AM 1.5, 100 mW/cm²). Further, each solar cellmodule was placed in a dark place at a temperature of 85° C. and ahumidity of 85% and maintained for 500 hours while a reverse bias of 10Vwas being applied. Thereafter, the photoelectric conversion efficiencywas again measured to examine a change in photoelectric conversionefficiency due to application of the reverse bias under high-temperatureand high-humidity conditions. Table 6 shows the results of thesemeasurements.

It can be understood that the substrates and the photovoltaic devicesusing the laminates in accordance with the present invention and thesolar cell modules including the substrates and the photovoltaic deviceshave improved qualities, as shown in Table 6. It can also be understoodthat the substrates, the photovoltaic devices and the solar cell modulesformed by setting the rate of formation of metal layer (C) 101-3C to avalue not higher than 4.0 nm/s have particularly improved qualities interms of reflectance, photoelectric conversion efficiency and theresults of the high-temperature and high-humidity reverse biasapplication test. Also, those formed by setting the rate of formation ofmetal layer (C) 101-3C to 0.5 nm/s or higher are particularlyadvantageous in terms of productivity since metal layer (C) 101-3C canbe formed in a shorter time in comparison with metal layer (B) 101-3B.

Example 9

Substrates and solar cell modules (Examples 9-1 to 9-4) were made in thesame manner as in Example 1 except that the rate of formation of metaloxide layer (A) 101-4A was changed to 0.03 nm/s, 0.05 nm/s, 3.0 nm/s,and 5.0 nm/s. The reflectance of the substrates thereby made wasmeasured with respect to light of 800 nm, and the photoelectricconversion efficiency of the solar cell modules was measured by usingthe solar simulator (AM 1.5, 100 mW/cm²). Further, each solar cellmodule was placed in a dark place at a temperature of 85° C. and ahumidity of 85% and maintained for 500 hours while a reverse bias of 10Vwas being applied. Thereafter, the photoelectric conversion efficiencywas again measured to examine a change in photoelectric conversionefficiency due to application of the reverse bias under high-temperatureand high-humidity conditions. Table 7 shows the results of thesemeasurements.

It can be understood that the substrates and the photovoltaic devicesusing the laminates in accordance with the present invention and thesolar cell modules including the substrates and the photovoltaic deviceshave improved qualities, as shown in Table 7. It can also be understoodthat the substrates, the photovoltaic devices and the solar cell modulesformed by setting the rate of formation of metal oxide layer (A) 101-4Ato a value not higher than 3.0 nm/s have particularly improved qualitiesin terms of reflectance, photoelectric conversion efficiency and theresults of the high-temperature and high-humidity reverse biasapplication test. Also, those formed by setting the rate of formation ofmetal oxide layer (A) 101-4A to 0.05 nm/s or higher are particularlyadvantageous in terms of productivity since metal oxide layer (A) 101-4Acan be formed in a shorter time in comparison with metal oxide layer (B)101-4B.

Example 10

A photovoltaic device shown in FIG. 6 was formed by a process describedbelow, using the semiconductor layer forming apparatus 201 shown in FIG.4. FIG. 6 is a schematic cross-sectional view of an example of aphotovoltaic device having the silicon thin film in accordance with thepresent invention. In FIG. 6, the same components as those shown in FIG.1 are indicated by the same reference characters. Description for thesame components will not be repeated. The semiconductor layer of thisphotovoltaic device is formed of amorphous n-type semiconductor layers102-1 and 102-4, an i-type semiconductor layer 102-2 containing acrystalline phase, an amorphous i-type semiconductor layer 102-5, andp-type semiconductor layers 102-3 and 102-6 each containing acrystalline phase. That is, this photovoltaic device is a pin-pin-typedouble-cell photovoltaic device.

A substrate 204 was made in the same manner as in Example 1 and mountedin the semiconductor layer forming apparatus 201, and the substratefeed-out container 202, the semiconductor layer forming vacuumcontainers 211 to 218 and the substrate take-up containers 203 wereevacuated to 1.0 mPa or lower by an evacuation system formed by a vacuumpump (not shown).

Subsequently, raw-material gases and diluent gases were supplied to thesemiconductor layer forming vacuum containers 211 to 218 through the gasintroducing pipes 231 to 238 while the evacuation system was beingoperated. Also, H₂ gas was supplied at 500 cm³/min (normal) to each gasgate through a gate gas supply pipe (not shown). In this state, thepressure in each of the semiconductor layer forming vacuum containers211 to 218 was adjusted to a desired pressure by adjusting theevacuation ability of the evacuation system. Forming was performed underthe same conditions as in the case of the method in Example 1 withrespect to the semiconductor forming vacuum containers 211 to 215, andthe conditions with respect to the semiconductor forming vacuumcontainers 216 to 218 were as shown in Table 8.

When the pressure in each of the semiconductor layer forming vacuumcontainers 211 to 218 was stabilized, the movement of theelectroconductive substrate 204 in the direction from the substratefeed-out container 202 toward the substrate take-up container 203 wasstarted.

Next, radiofrequency waves were introduced from radiofrequency powersupplies 251 to 258 to radio frequency wave introducing portions 241 to248 in the semiconductor forming vacuum containers 211 to 218 to causeglow discharge in forming chambers in the semiconductor layer formingvacuum containers 211 to 218, thereby forming on the electroconductivesubstrate 204 an amorphous n-type semiconductor layer (50 nm thick), ani-type semiconductor layer (1.5 μm thick) containing a crystallinephase, a p-type semiconductor layer (10 nm thick) containing acrystalline phase, an amorphous n-type semiconductor layer (30 nmthick), an amorphous i-type semiconductor layer (300 nm thick) and ap-type semiconductor layer (10 nm thick) containing a crystalline phase.The photovoltaic device was thus formed.

In this process, radiofrequency power at a frequency of 13.56 MHz and apower density of 5 mW/cm³ was introduced into the semiconductor formingvacuum containers 211 and 216, radiofrequency power at a frequency of 60MHz and a power density of 300 mW/cm³ into the semiconductor formingvacuum containers 212 to 214, radiofrequency power at a frequency of13.56 MHz and a power density of 30 mW/cm³ into the semiconductorforming vacuum containers 215 and 218, and radiofrequency power at afrequency of 60 MHz and a power density of 50 mW/cm³ into thesemiconductor forming vacuum container 217. The band-like photovoltaicdevice thus formed was worked into 36×22 cm solar cell modules by usingcontinuous modulation apparatus (not shown) (Example 10).

The photoelectric conversion efficiency of the solar cell module thusmade was measured by using the solar simulator (AM 1.5, 100 mW/cm²). Themeasured value of the photoelectric conversion efficiency was 1.15 timeshigher than that of the single solar cell module in Example 1. Favorableresults are also obtained with respect to the peeling test and thetemperature and humidity test. From the above, it can be understood thatthe substrate and the photovoltaic device using the laminate inaccordance with the present invention and the solar cell moduleincluding the substrate and the photovoltaic device have improvedqualities.

Example 11

Intermediate layer 101-2, metal layer (A) 101-3A, metal layer (B)101-3B, metal layer (C) 101-3C, and metal oxide layer (A) 101-4A wereformed in the same manner as in Example 1 by using the metal layer/metaloxide layer forming apparatus shown in FIG. 3, and metal oxide layer (B)101-4B was thereafter formed by using a metal oxide layer formingapparatus shown in FIG. 7, thereby making a substrate.

FIG. 7 is a schematic cross-sectional view of an example of a metaloxide layer forming apparatus 701 for manufacturing the substrate of thephotovoltaic device of the present invention. The metal oxide layerforming apparatus 701 shown in FIG. 7 is constituted by a feed-outroller 702, a metal oxide layer forming container 711, a water cleansingcontainer 713, a drying container 715, and a take-up roller 703. Aband-like base member 704 is set in this metal oxide layer formingapparatus 701 so as to extend through each container. The band-like basemember 704 is unwound from a bobbin placed at the feed-out roller 702and is wound around another bobbin by the take-up roller 703. A counterelectrode 721 made of zinc is provided in the metal oxide layer formingcontainer 711, and is connected to a load resistor (not shown) and apower supply 731.

The temperature of an aqueous solution in the metal oxide layer formingcontainer 711 can be monitored and adjusted by using a heater and athermocouple (both not shown). In the water cleansing container 713, theaqueous solution on the substrate surface is washed away by using anultrasonic device (not shown), pure water cleansing is performed byusing a pure water shower 714 at the exit side of the water cleansingcontainer. In the drying container 715, the substrate surface can bedried by using an infrared heater 716.

When the aqueous solution in the metal oxide layer forming container 711had a zinc ion concentration of 0.2 mol/l, pH=5.0, an aqueous solutiontemperature of 80° C., and a dextrin concentration of 0.05 g/l,conveyance of the base member was started and forming of metal oxidelayer (B) made of a zinc oxide was performed. At this time, the densityof current flowing through the counter electrode 721 was 200 mA/dm² andthe zinc oxide forming rate was 10 nm/s.

A pin-pin-type double-cell solar module (Example 11) similar to Example10 was made by using the band-like substrate formed as described above.

The solar cell module made in Example 11 was excellent in adhesion,initial conversion efficiency, and durability with respect to thetemperature and humidity test and the high-temperature high-humidityreverse bias application test. From the above, it can be understood thatthe substrate and the photovoltaic device using the laminate of thepresent invention and the solar cell module including the substrate andthe photovoltaic device have improved qualities.

TABLE 1 311 forming Raw-material gas Ar: 50 cm³/min (normal) conditionsTemperature of formation 400° C. surface Pressure 0.3 Pa Sputteringpower 0.5 KW 312 forming Raw-material gas Ar: 50 cm³/min (normal)conditions Temperature of formation 400° C. surface Pressure 0.3 PaSputtering power 0.4 KW 313 forming Raw-material gas Ar: 50 cm³/min(normal) conditions Temperature of formation 400° C. surface Pressure0.3 Pa Sputtering power 3.0 KW 314 forming Raw-material gas Ar: 50cm³/min (normal) conditions O₂: 10 cm³/min (normal) Temperature offormation 350° C. surface Pressure 0.3 Pa Sputtering power 0.4 KW 315forming Raw-material gas Ar: 50 cm³/min (normal) conditions O₂: 10cm³/min (normal) Temperature of formation 350° C. surface Pressure 0.3Pa Sputtering power 1.0 KW 316 forming Raw-material gas Ar: 50 cm³/min(normal) conditions Temperature of formation 350° C. surface Pressure0.3 Pa Sputtering power 7.0 KW

TABLE 2 211 forming Raw-material gas SiH₄: 20 cm³/min (normal)conditions H₂: 100 cm³/min (normal) PH₃ (Diluted to 2% with H₂): 30cm³/min (normal) Temperature of formation 300° C. surface Pressure 100Pa 212 to 214 Raw-material gas SiH₄: 30 cm³/min (normal) forming SiF₄:100 cm³/min (normal) conditions H₂: 500 cm³/min (normal) Temperature offormation 300° C. surface Pressure 100 Pa 215 forming Raw-material gasSiH₄: 10 cm³/min (normal) conditions H₂: 800 cm³/min (normal) BF₃(Diluted to 2% with H₂): 100 cm³/min (normal) Temperature of formation200° C. surface Pressure 150 Pa

TABLE 3 Example Example Example Example Example Comparative Comparative1 2 3 4 5 Example 1 Example 2 Reflec- Total 1 0.96 0.95 1.01 0.98 0.960.90 tance reflec- tion Diffused 1 0.97 0.95 0.98 1.00 0.89 0.90 reflec-tion Grid tape method 1 0.98 0.97 0.96 0.98 0.81 0.95 Average value of 10.97 0.96 1.01 1.00 0.90 0.91 photoelectric conversion efficiencyUniformity of 1 1.02 1.05 1.04 1.06 1.20 1.08 photoelectric conversionefficiency Change in 1.0 1.0 0.97 0.96 0.95 0.88 0.92 photoelectricconversion efficiency due to high- temperature high-humidity biasapplication test

The reflectivity is standardized with respect to the value in Example 1shown as 1.

The value in the grid tape method is standardized with respect to thenumber of squares not peeled in Embodiment 1, shown as 1.

The average of the photoelectric conversion efficiency is standardizedwith respect the value in Example 1 shown as 1.

The uniformity of the photoelectric conversion efficiency isstandardized with respect the value of the standard deviation in Example1 shown as 1.

The change in photoelectric conversion efficiency due to thehigh-temperature high-humidity reverse bias test is the value of theefficiency after the test/the initial efficiency.

TABLE 4 Photo- Reflectance electric Thickness of Total Diffused conver-intermediate reflec- reflec- Grid tape sion layer tion tion methodefficiency Comparative  0 nm 0.92 0.89 0.81 0.90 Example 1 Example 6-110 nm 0.95 0.92 0.96 0.95 Example 6-2 30 nm 1.02 0.98 1 0.98 Example 150 nm 1 1 1 1 Example 6-3 80 nm 1.03 0.98 1 1.02 Example 6-4 100 nm 0.98 1.02 1 1.00 Example 6-5 150 nm  0.96 0.98 1 0.96

The reflectivity is standardized with respect to the value in Example 1shown as 1.

The value in grid tape method is standardized with respect to the numberof squares not peeled in Embodiment 1, shown as 1.

The photoelectric conversion efficiency is standardized with respect tothe value in Example 1 shown as 1.

TABLE 5 Change in photoelectric conversion Rate of Reflectance Photo-efficiency due to formation Total Diffused electric high-temperature ofmetal reflec- reflec- conversion high-humidity bias layer (A) tion tionefficiency application test Example 7-1 0.3 nm/s 1.0 0.98 0.98 1.0Example 7-2 0.5 nm/s 1.02 1.0 1.0 1.0 Example 7-3 1.0 nm/s 1.02 0.980.98 1.0 Example 1 1.5 nm/s 1 1 1 1.0 Example 7-4 2.0 nm/s 1.0 1.0 1.01.0 Example 7-5 4.0 nm/s 1.0 0.98 1.0 1.0 Example 7-6 5.0 nm/s 0.97 0.980.96 0.97

The reflectivity is standardized with respect to the value in Example 1shown as 1.

The photoelectric conversion efficiency is standardized with respect tothe value in Example 1 shown as 1.

The change in photoelectric conversion efficiency due to thehigh-temperature high-humidity reverse bias test is the value of theefficiency after the test/the initial efficiency.

TABLE 6 Change in photoelectric conversion efficiency due to Rate ofReflectance Photo- high-temperature formation Total Diffused electrichigh-humidity of metal reflec- reflec- conversion bias application layer(C) tion tion efficiency test Example 8-1 0.3 nm/s 1.02 1.0 1.0 1.0Example 8-2 0.5 nm/s 1.0 0.98 0.98 1.0 Example 8-3 1.0 nm/s 1.04 0.980.98 1.0 Example 1 1.5 nm/s 1 1 1 1.0 Example 8-4 2.0 nm/s 1.0 1.02 1.01.0 Example 8-5 4.0 nm/s 1.0 1.0 1.0 1.0 Example 8-6 5.0 nm/s 0.98 0.960.96 0.98

The reflectivity is standardized with respect to the value in Example 1shown as 1.

The photoelectric conversion efficiency is standardized with respect tothe value in Example 1 shown as 1.

The change in photoelectric conversion efficiency due to thehigh-temperature high-humidity reverse bias test is the value of theefficiency after the test/the initial efficiency.

TABLE 7 Change in photoelectric conversion Rate of efficiency due toformation Reflectance Photo- high-temperature of metal Total Diffusedelectric high-humidity oxide reflec- reflec- conversion bias applicationlayer (A) tion tion efficiency test Example 9-1 0.03 nm/s 0.96 1.0 0.981.0 Example 9-2 0.05 nm/s 1.0 0.98 0.98 1.0 Example 9-3  0.1 nm/s 1.020.98 1.0 1.0 Example 1  1.0 nm/s 1 1 1 1.0 Example 9-4  3.0 nm/s 1.021.02 1.04 1.0 Example 9-6  5.0 nm/s 0.96 0.96 0.95 0.98

The reflectivity is standardized with respect to the value in Example 1shown as 1.

The photoelectric conversion efficiency is standardized with respect tothe value in Example 1 shown as 1.

The change in photoelectric conversion efficiency due to thehigh-temperature high-humidity reverse bias test is the value of theefficiency after the test/the initial efficiency.

TABLE 8 216 Raw-material gas SiH₄: 20 cm³/min (normal) forming H₂: 100cm³/min (normal) conditions PH₃ (Diluted to 2% with H₂): 50 cm³/min(normal) Temperature of 300° C. formation surface Pressure 100 Pa 217Raw-material gas SiH₄: 300 cm³/min (normal) forming H₂: 4000 cm³/min(normal) conditions Temperature of 300° C. formation surface Pressure800 Pa 218 Raw-material gas SiH₄: 10 cm³/min (normal) forming H₂: 800cm³/min (normal) conditions BF₃ (Diluted to 2% with H₂): 100 cm³/min(normal) Temperature of 200° C. formation surface Pressure 160 Pa

The laminate formed according to a preferred embodiment of the presentinvention and the photovoltaic device using the laminate as a substratehave improved characteristics and maintain improved reflectioncharacteristics and adhesion under high-temperature and high-humidityconditions and during long-term use.

1. A method of forming a laminate, comprising a first step of forming anintermediate layer on a base member, and a second step of forming ametal layer on the intermediate layer, the adhesion of the metal layerto the base member being lower than that of the intermediate layer, thereflectance of the metal layer being higher than that of theintermediate layer, wherein the rate of formation of the metal layer isincreased at an intermediate stage in said second step.
 2. The methodaccording to claim 1, wherein the intermediate layer is formed to athickness within the range of 30 nm to 100 nm on the base member.
 3. Themethod according to claim 1, wherein the rate of formation of the metallayer before increasing the formation rate is set within the range of0.5 nm/s to 4.0 nm/s.
 4. The method according to claim 1, wherein therate of formation of the metal layer is increased at a point in timewhen the metal layer is formed to a thickness within the range of 1 nmto 100 nm on the intermediate layer.
 5. A method of manufacturing aphotovoltaic device, comprising a first step of forming an intermediatelayer on a base member, a second step of forming a metal layer on theintermediate layer, the adhesion of the metal layer to the base memberbeing lower than that of the intermediate layer, the reflectance of themetal layer being higher than that of the intermediate layer, and athird step of forming a semiconductor layer directly on the metal layeror with a metal oxide layer interposed between the semiconductor layerand the metal layer, wherein the rate of formation of the metal layer isincreased at an intermediate stage in said second step.